Pyranoside is a compound that results from the glycosylation of pyranose (sugar) with an alcohol such as a naturally occurring steroid. Pyranoside has two isomers: α-O-pyranoside and β-O-pyranoside. Among them, β-O-pyranoside is an important compound having various bioactivities.
General chemical synthesis to produce pyranoside provides a mixture of α-O-pyranoside and β-O-pyranoside; therefore, it is impossible to produce β-O-pyranoside selectively by such chemical synthesis.
It is, however, possible to produce β-O-pyranoside selectively by applying neighboring group participation using a sugar donor in which the 2-position of the sugar is protected with an acyl group (Non-Patent Literatures 1 to 5). However, this method has a drawback such that the electron withdrawing property of the acyl group decreases the glycosylation speed. Moreover, this method cannot be applied when the acyl group cannot be introduced into the 2-position of the sugar.
Accordingly, there has been a demand for development of a new method which enables selective β-expression without applying the neighboring group participation, particularly, the development of a process for easily producing a corresponding β-O-pyranoside at a high selectivity and a high yield without requiring strict reaction conditions, even when various alcohols are used in the reaction; and a demand for development of a new pyranose donor (β-O-glycosylating agent) to be used in such a process.
[Non-patent Literature 1]
    Love, K. R., Andrade, R. B., Seeberger, H. P. J. Org. Chem., 2001, 66, pp. 8165-8176[Non-patent Literature 2]    Boons, G. J. Contemp. Org. Synth., 1996, 3, pp. 173-200[Non-patent Literature 3]    Kunz, H., Harreus, A. Liebigs Ann. Chem., 1982, pp. 41-48[Non-patent Literature 4]    Garegg. J. P., Norberg, T. Acta. Chem. Scand. B., 1979, 33, pp. 116-118[Non-patent Literature 5]    Koenigs. W., Knorr, E. Chem. Ber., 1901, pp. 957-981